The invention concerns a cylinder mill to grind a granular product, such as grain, etc. into flour, cracked grain, semolina, etc. It especially concerns the overdrive of such cylinder mills with at least one pair of rollers with corrugated or smooth rollers.
Cylinder mills to grind grain contain at least two or four pairs of rollers as described in DE-C-2730166 or as described in EP-B-334919. The rollers of a roller pair rotate in the opposite direction and with at different speeds to crush and mill the grains. The roller gap can usually be varied.
Normally the faster-running roller is driven and connected to the slower-running roller with an overdrive. Such an overdrive is primarily constructed in the form of gearing that, however, must be lubricated, is very loud, and requires exchange gears to adapt to milling conditions which can differ widely. For quite a while, there has been an attempt to overcome the disadvantages of gears by using smooth or contoured belts. In addition to solutions using a V-belt, belts with teeth on both sides (e.g. U.S. Pat. No. 3,338,107) or multiple V toothed belts (e.g. TIMING-VEE) were developed. For example, DEAS 1107033 describes a combination V-belt and toothed belt with a toothed side and a V-shaped side of the belt that runs between three toothed belt pulleys, and that also drives an outer V-belt pulley.
A similar solution for a cylinder mill is described in DE-A-3304832. The double-sided toothed belt runs around belt pulleys of the rollers, and also runs around a toothed belt pulley of the drive and an idler pulley.
GB-A-1460628 discloses a belt drive for variable speeds with an adjustable guide pulley for 2 belts on a movable slide in a swinging arm. Any imprecision of the arm alignment can be corrected by cam disks on the rotary axes.
There is another prior-art toothed-belt overdrive that uses toothed V-belts found in ITPS 1198054 and EP-B-425626, and WO-A-90/14161. The latter describes a cylinder mill with at least one roller pair. The shaft of the slower-running roller carries a pulley that has teeth with notches parallel to the axis and includes a driving device, which is kept under tension by a third driving pulley with an adjustable position. The whole pulley is adjustable using regulating screws or an eccentric. The faster running roller is also equipped with a pulley that has teeth with notches. But these are arranged at right angles to the shaft axis. The driving device itself is a belt treaded on the outside and inside, which engages snugly in the profiles of the above mentioned three pulleys, meaning with a tooth or spline profile.
The width of the pulleys is designed, so that normally three belts can be put on parallel in order to increase the power to be transmitted. According to the state of the art mentioned above these are tightened simultaneously and wear out differently. It is very labour-consuming and not entirely possible to tighten the belts evenly. The problems can not be solved even by previous assessment and measuring.
The invention is therefore based on the task of avoiding the illustrated disadvantages of the state of the art, and therefore achieving an even tension of the individual belts and consequently an even wear.
The applicant""s studies showed that the inner belt or inner belt parts, respectively, tend to wear out first due to the strain of the grinding rolls, which can not be avoided in the operating state. As a result any assessment or measuring of belts will be at least partially ineffective. It is rather important to observe these different conditions of wear. According to the invention a parted pulley (idler pulley) is therefore designed in order to tighten the belts individually. Preferably this pulley is partially divided into two sections.
More in-depth studies by the applicant showed that the assumed maximum transmission performance could not be achieved in practice. Therefore it normally seems unnecessary to use three or more belts. This also makes adjustment easier.